<template>
	<ul class="Alphabet">
		<li 
		class="item" 
		v-for='item in letter' 
		:key='item'
		:ref='item'
		@touchstart.prevent='handleTouchStart '
		@touchmove='handleTouchMove'
		@touchend='handleTouchEnd'
		@click='handleClick'
		>{{item}}</li>	
	</ul>
</template>

<script>
export default {	
	name: 'Alphabet',
	props: {
		cities: Object
	},
	data () {
		return {
			touchStatus: false,
			startY: 0,
			timer: null
		}
	},
	computed: {
		letter () {
			const letters = []
			for (let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	updated () {
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleClick (e) {
			this.$emit('change', e.target.innerText)
		},
		handleTouchStart () {
			this.touchStatus = true
		},
		handleTouchMove (e) {
			if (this.touchStatus) {
					if (this.timer) {
						clearTimeout(this.timer)
					}
					this.timer = setTimeout( () => {
						const touchY = e.touches[0].clientY - 79
						const index = Math.floor((touchY - this.startY) / 20)
						if (index >= 0 && index < this.letter.length) {
						this.$emit('change', this.letter[index])
						}
					}, 16)	
				
			}
		},
		handleTouchEnd () {
			this.touchStatus = false
		}
	}
}	
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
	.Alphabet
		position: absolute
		right: 0
		top: 1.58rem
		bottom: 0
		width: .4rem
		display: flex
		flex-direction: column
		justify-content: center
		.item
			text-align: center
			line-height: .4rem
			color: $bgColor
			
			
</style>